Introduction:
Sulphate ions are a part of the earth’s crust and usually occur in natural waters. Many sulphate compounds are readily soluble in water. Most of them originate from the oxidation of sulphate ores, the solution of gypsum and anhydrite, the presence of shales, particularly those rich in organic compounds, and the existence of industrial wastes. Atmospheric sulphur dioxide formed by the combustion of fossil fuels and emitted by the metallurgical roasting processes may also contribute to the sulphate compounds of water. Sulphur trioxide (SO3) produced by the photolytic oxidation of sulphur dioxide comes with water vapours to form sulphuric acid which is precipitated as acid rain or snow. Sulphur-bearing mineral are common in most …show more content…
(ii) Buffer B (required when the sample SO4 2- concentration is less than 10 mg / l): Dissolve 30 g MgCl2. 6H2O, 5 g sodium acetate, CH3COONa. 3 H2O, 1.0 g potassium nitrate KNO3, 0.111 g sodium sulphate, Na2SO4, and 20 ml acetic acid (99%) in 500 ml distilled water and make up 1000 ml. (iii) Barium Chloride …show more content…
R. grade) in distilled water and make up to 1000 ml. 1.0 ml = 100 µg SO4 2-

Preparation of blank, standard and sample solutions
• Take six 50 ml flasks (4 for standard, 1 for blank and 1 for sample).
• The standards are prepared at 5mg/L increments in 0-40 mg/L sulphate range. Beyond 40mg/L accuracy decreases and barium sulphate loses stability.
• To the fifth flask (sample flask) add sample
• To the sixth flask (blank flask) add only distilled water. Do not add barium chloride to it because absorbance for blank is taken to correct for sample color and turbidity.
Procedure :-
(i) Use spectrophotometer at 420 nm.
(ii) Measure 100 ml sample in 250 ml Erlenmeyer flask
(iii) Add 20 ml buffer solution (A or B) and mix on a magnetic stirrer approach
(iv)While stirring, add a spoonful of barium chloride BaCl2 crystals and start observing time immediately. (v) Stir for 60 ± 2 sec at a constant speed. (vi) Immediately, take reading at 420 nm. The value of blank sample should be deducted from all the standard and sample reading to get final